Bulimia nervosa (BN) is a serious mental illness marked by substantial medical and psychiatric morbidity. Although cognitive-behavioral therapy (CBT) is the treatment of choice for BN, dissemination of this evidence-based approach has been suboptimal, with the majority of individuals requiring care never receiving treatment. Moreover, up to one-third of individuals relapse after CBT, indicating the need for maintenance interventions. Thus the evaluation of new strategies for dissemination of CBT and the development of novel interventions to maximize maintenance of treatment benefits are critical to improve our ability to treat BN. Optimizing technology is a logical next step to move the field forward and enhance public health reach. Thus in this application, in response to PA-07-295: Information Technologies and the Internet in Health Services and Intervention Delivery (R01), we seek to determine whether CBT delivered via the internet with moderated chat-group support is as effective as is face-to-face group CBT. We propose to randomize 180 patients to either standard face to face group CBT (the gold standard) or CBT via the internet (CBT.net) in a two-site, 20 week acute treatment trial. Treatments will be compared on measures of attrition, adherence, acceptability, binge and purge frequency, abstinence, and cost effectiveness. Specifically, we hypothesize that CBT.net will not be inferior to group CBT on primary outcome measures and that it will be more cost-effective. All participants will be followed up at three, six, and twelve months following completion of the acute treatment. This trial will utilize an internet based program for BN developed by Dr. Bulik (R21MH070781 "Web-based Cognitive Therapy for Bulimia Nervosa"). Successful completion of this project will provide critical information about the provision of treatment via the internet for patients who do not have access to evidence-based care. If CBT delivered via the internet is similarly efficacious to that delivered in the standard face to face group format, results of the proposed would have the potential to yield a cost- effective strategy to disseminate evidence-based treatments for BN. The purpose of this study is to compare an internet-delivered cognitive-behavioral treatment (CBT) program for bulimia nervosa with standard group CBT. If effective, CBT via the internet could be a cost-effective strategy to disseminate evidence-based treatments for BN.